Flame control in furnace burners

ABSTRACT

Flame control in furnace burners has previously lacked any means for sensing the position of the apex of the combustion with respect to the entry throat of the burner. This has resulted in inefficient combustion and, in certain cases, explosions resulting from the fact that the flame may be extinguished during operation of the burner. This invention provides a simple and effective apparatus for detecting and locating the apex of the burner flame within the throat of the combustion chamber. The flame sensing means is adapted to detect the position of the apex of the flame with respect to the throat of the burner and control means is provided which is responsive to the flame sensing means for controlling the forward velocity of the air admitted.

[ Sept. 30, 1975 FLAME CONTROL IN FURNACE BURNERS Arnold M. Earl, 1325 Applewood Rd., Mississauga, Ontario, Canada, LSE 2L9 [22] Filed: Oct. 15, 1974 121] Appl No.: 514,424

[76] Inventor:

[301 Foreign Application Priority Data Primary liramincr-Edward G. Favors Attorney, Agent, or Firm-Fetherstonhaugh & Co.

[57] ABSTRACT Flame control in furnace burners has previously lacked any means for sensing the position of the apex of the combustion with respect to the entry throat of the burner. This has resulted in inefficient combustion and, in certain cases, explosions resulting from the fact that the flame may be extinguished during operation of the burner. This invention provides a simple and effective apparatus for detecting and locating the apex of the burner flame within the throat of the combustion chamber. The flame sensing means is adapted to detect the position of the apex of the flame with respect to the throat of the burner and control means is provided which is responsive to the flame sensing means for controlling the forward velocity of the air admitted.

3 Claims, 3 Drawing Figures Sept. 30,1975 Sheet 1 of 2 $909,184

n e t a P S US. Patent Sept. 30,1975 Sheet 2 of2 3909,14

FIGQ

.1 1 1 r I .l I II I I FLAME CONTROL IN FURNACE BURNERS This invention relates to the combustion of fuels in boilers and the like. In particular, this invention relates to improvements in the control of the flame in the combustion chamber of a boiler.

The lack of proper controls for burners of furnaces and boilers has resulted in all to frequent explosions in this type of equipment. The explosions usually result from the fact that the fuel combustion flame or flames are temporarily extinguished, permitting an accumulation of eombustable fuel in the combustion chamber which explodes when a critical mixture is attained or on relighting of the combustion flame. Explosions may also result from the incomplete combustion of fuel which accumulates in an area in a furnace outwardly from the combustion chamber. In boilers, an explosion may result from the accumulation of the products of incomplete combustion in the secondary heat exchange zones of the boiler.

It is well established that it is important to attempt to complete the combustion of the fuel in the principal combustion area of the boiler. In current boiler construction, attempts to obtain substantially complete combustion of the fuel has resulted in the extension of the combustion into areas of the boiler which are removed from the principal combustion area. While this does increase the overall efficiency of the boiler, it substantially increases the likelihood of an accumulation of incompletely combusted fuel in the areas remote from the principal combustion area. The incompletely combusted fuel is eventually discharged to the atmosphere in the form of pollution which is both visible and invisible.

The most efficient combustion is achieved when the apex of the combustion flame is located in the throat of the burner. In order to achieve an efficient combus tion, it is normal practice to provide an excess of combustion air. The so-called circular burners" are most frequently used in modern boiler installations. The circular burners include a wind-box and control means for controlling the proportion of the air which enters the furnace throat in a direction longitudinally of the throat and the proportion which enters the throat generally tangentially of the throat. The tangential or rotational air flow serves to provide an excess of combustion air without tending to blow the flame outwardly from the throat. While previous burner controls have included flame sensing means for detecting whether or not a burner is ignited, these known sensing means have been arranged to view the throat area of the burner in a direction longitudinally of the throat. The longitudinally oriented detecting means of the prior art is only capable of detecting whether or not the burner is ignited. The known detecting means does not provide any indication as to the position of the apex of the flame with respect to the throat area of the combustion chamber. As previously indicated. incomplete combustion of the fuel may result when combustion does not take place in the principal combustion area of the combustion chamber and combustion can only take place in the principal combustion area when the apex of the flame is located within the throat area of the combustion chamber.

The present invention overcomes the difficulties of the prior art described above and provides a simple and efficient apparatus for detecting the location of the apex of the burner flame within the throat of the combustion' chamber. The flame sensing means is adapted to detect the position of the apex of the flame with respect to the throat of the burner.

According to an embodiment of the present invention, an apparatus for burning fuel comprising a boiler, the boiler having a combustion chamber and the combustion chamber having a principal combustion area and a throat through which fuel and air enter the principal combustion area. The apparatus also includes means for admitting fuels through the entry throat to the combustion area and means at the entry throat for controlled admission of the entry air through the entry throat to the combustion area in a direction rotationally and/or longitudinally of the throat. In addition, flame sensing means is provided in the entry throat for sensing light from the apex of combustion in a direction that extends transversely of the entry throat.

The invention will be more clearly understood after reference to the following detailed specification read in conjunction with the drawings.

In the drawings:

FIG. 1 is a pictorial view illustrating a boiler of a type in which a flame detection means of the present invention are used;

FIG. 2 is an enlarged sectional view taken on the line 22 of FIG. 1; and

FIG. 3 is a pictorial view illustrating the controls for controlling the flow of air through the burner throat.

With reference to the drawings, the reference numeral 10 refers generally to a boiler of a type in which the burner controls of the present invention may be used. The boiler may employ pulverized coal burners, oil burners or the like. A typical boiler in which the burner control of the present invention may be used is a standard water tube boiler of the type manufactured by Bamcox & Wilcox Limited For example, a B & W furnace identified by the trade name The furnace 10 has a wind-box 12 which supplies combustion air to a plurality of burners 14. The burners 14 are of a type known as a circular" burner and a typical burner of this type is manufactured by Babeox & Wilcox and known in the trade as a B & W Circular Burner. The circular burners are particularly suitable for use in the combustion of pulverized coal as shown in FIG. 3 of the drawings. The burner 14 consists of a burner tube 16 which has its outer and mounted in an opening in the wall of the wind-box 12. The inner end of the burner is centrally located with respect to the burner throat 18 which is formed in the wall of the boiler by deformation ofthe water tubes 20. A plurality of vanes 22 are mounted within the wind-box 12 at circumferentially spaced intervals about the burner 14. The vanes 22 are mounted for movement on an axle 24 so as to be movable from a position in which substantially all of the air admitted to the burner from the wind-box will be directed circumferentially of the axis of the burner and a second position in which a major portion of the air entering the burner will discharge from the burner generally axially of the longitudinal axis of the burner. This adjustment is used in order to control the position of the apex of the combustion flame. By increasing the proportion of the combustion air which is admitted tangentially, the longitudinal velocity of the flame is decreased and the apex of the flame will move towards the discharge end of the burner. By decreasing the amount of circumferential air and increasing the amount of axially discharging air, the longitudinal velocity of the flame may be increased so that the apex of the flame is moved away from the.

discharge end of the burner. This is a characteristic of the known type of burner described above and does not in itself constitute a part of the present invention.

The present invention is more clearly illustrated with reference to FIG. 2 of the drawings. As shown in FIG. 2 of the drawings, the throat 18 which is formed in the wall of the boiler is lined with a refractory material 26.

The principal combustion area 28 of the boiler is located directly outwardly from the throat 18. As previously indicated, it is important to ensure that substan tially complete combustion of the fuel has been established prior to discharge of the combustion mixture from the principal combustion area to the apex. In order to ensure that the required combustion is obtained in the principal combustion area, it is necessary to ensure that the apex of the combustion flame is located within the throat 18 of the burner. If the longitudinal velocity of the air admitted to the burner throat is too great, the apex of the flame will be located out wardly from the burner throat and combustion will extend into the areas of the furnace which are not designed to accommodate combustion and therefore result in the decreased overall efficiency. If the longitudinal velocity of the flame is so slow that it is located directly at the inner end of the burner, it is likely that insufficient air is being provided to ensure complete combustion.

In order to determine the location of the apex of the flame during combustione, the present invention provides a first sensing means 38 for sensing the light from the apex of combustion in a direction that extends transverse to the throat at the entry end of the throat. The present invention also provides second sensing means 46 for sensing the light from the apex of combustion in a direction transversely of the exit end of the throat at the exit end of the entry throat. The first sensing means 38 includes a sensing tube 32 and prisms 34 and 36 and the second sensing means includes sensing tube 40 and prisms 42 and 44. The tubes 32 and 40 are embedded in the refractory walls of the throat and a passage 37 opens from the prism 36 through the refractory wall to limit light to pass to the prism 36. The light which is transmitted by the prisms 36 and 34 along the tube 32 is detected by suitable detector means 38. Similarly, the second sensing means includes a tube 40 and prisms 42 and 44. The light which is reflected by the prisms 42 and 44 is measured by a detecting device 46. The prism 36 is designed to deflect light detected along the path of the broken line 58 and the prism 42 is adapted to detect the light along the path of the broken line 60. The path 58 extends transversely of the entry end of the entry throat adjacent to the output end of the burner tube 16 while the path 60 extends transversely of the entry throat adjacent to the exit end of the entry throat. If the first sensing device senses the light of the apex of combustion located atthe output end of the burner, the burner air register drive means is activated to move the register vanes to a position to decrease the amount of tangential air to thereby increase the longitudinal velocity of the air admitted to the burner. This causes the apex of the flame to move away from the output end of the burner into the area of the throat 18. lf the second sensing means detects the presence of the apex of combustion along the path 60 which is at the exit end of the throat, the burner air register drive means operates in reverse to reduce the forward velocity and increase the rotational velocity of the air admitted to the burner.

Sensing means such as those identified above by the reference numerals 46 and 38 are presently available and are used in association with a sight tube for detecting whether or not a burner is properly ignited. A de- I vice of this type generally identified by the reference numeral 64 is employed in the burner of the present invention in conjunction with the first and second sensing devices previously described and is hereinafter referred to as the third sensing device 64. The third sensing device 64 consists of a sight tube 66 and a sensing means 68. It will be understood that the sensing devices 38 and 46 are adapted to distinguish between the light generated by the apex of the flame and the glow of the refractory material which aligns the throat.

As previously indicated, in operation the third sensing device 64 detects the presence of the flame while the first and second sensing devices serve to retain the flame in a position with the apex located within the throat area 18. The apex of the flame is moved away from the end of the burner 16 by increasing the proportion of the air admitted to the burner which has a substantial linear component and the apex of the flame is moved inwardly of the throat by increasing the proportion of the combustion air which is admitted tangentially of the burner throat.

From the foregoing, it will be apparent that the present invention provides a simple and inexpensive form of sensing means which may be used to accurately locate the apex of the flame.

Various modifications of the present invention will be apparent to those skilled in the art without departing from the scope of the invention. For example, the structure and construction of the sensing means may be modified to any suitable form. The prisms of the sensing means may be replaced by mirrors or mirrored surfaces or the like.

What I claim as my invention is:

l. Apparatuss for burning fuel comprising a. a boiler,

b. said boiler having a combustion chamber,

0. said combustion chamber having a principal combustion area and a throat through which fuel and air enter said principal combustion area, said throat having refractory walls,

(1. means for admitting fuel through said entry throat to said combustion area,

e. means at said entry throat for the controlled admitting of said air through said entry throat to said principal combustion area ina direction rotationally and/or longitudinally of said throat,

f. flame sensing means in said throat for sensing the light from the apex of combustion in the direction that extends transversely of said entry throat, and

h. control means responsive to said flame sensing means for controlling the forward velocity of air admitted by said means for admitting air.

2. An apparatus as claimed in claim 1 wherein said flame sensing means includes first flame sensing means at the entry in said entry throat and second sensing means at the exit end of the said entry throat.

3. An apparatus as claimed in claim 2 including third flame sensing means adjacent the entry end of said threat for sensing the light emission from the apex of combustion in the longitudinal direction of said throat. l =l 

1. Apparatuss for burning fuel comprising a. a boiler, b. said boiler having a combustion chamber, c. said combustion chamber having a principal combustion area and a throat through which fuel and air enter said principal combustion area, said throat having refractory walls, d. means for admitting fuel through said entry throat to said combustion area, e. means at said entry throat for the controlled admitting of said air through said entry throat to said principal combustion area in a direction rotationally and/or longitudinally of said throat, f. flame sensing means in said throat for sensing the light from the apex of combustion in the direction that extends transversely of said entry throat, and h. control means responsive to said flame sensing means for controlling the forward velocity of air admitted by said means for admitting air.
 2. An apparatus as claimed in claim 1 wherein said flame sensing means includes first flame sensing means at the entry in said entry throat and second sensing means at the exit end of the said entry throat.
 3. An apparatus as claimed in claim 2 including third flame sensing means adjacent the entry end of said throat for sensing the light emission from the apex of combustion in the longitudinal direction of said throat. 